1. Field of the Invention
This invention relates to a color cathode-ray tube (CRT) and, more particularly to a color CRT including a focus mask.
2. Description of the Background Art
A color cathode-ray tube (CRT) typically includes an electron gun, an aperture mask, and a screen. The aperture mask is interposed between the electron gun and the screen. The screen is located on an inner surface of a faceplate of the CRT tube. The screen has an array of three different color-emitting phosphors (e.g., green, blue, red) formed thereon. The aperture mask functions to direct electron beams generated in the electron gun toward appropriate color emitting phosphors on the screen of the CRT tube.
The aperture mask may be a focus mask. Focus masks typically comprise two sets of conductive lines (or wires) that are arranged orthogonal to each other, to form an array of openings. Different voltages are applied to the two sets of conductive lines so as to create multipole focusing lenses in each opening of the mask. The multipole focusing lenses are used to direct the electron beams toward the color-emitting phosphors on the screen of the CRT tube.
One type of focus mask is a tensioned focus mask, wherein at least one of the two sets of conductive lines is under tension. Typically, for tensioned focus masks, the vertical set of conductive lines is under tension, with the horizontal set of conductive lines overlying such vertical tensioned lines.
Where the two sets of conductive lines overlap, such conductive lines are typically attached at their crossing points (junctions) by an insulating material. When the different voltages are applied between the two sets of conductive lines of the mask, to create the multipole focusing lenses in the openings thereof, high voltage (HV) flashover may occur at one or more junctions. HV flashover is the discharge of an electrical charge across the insulating material separating the two sets of conductive lines. HV flashover is undesirable because it may cause an electrical short circuit between the two sets of conductive lines leading to the subsequent failure of the focus mask.
When the electron beams from the electron gun are directed toward the color-emitting phosphors on the screen, the electron beams may cause the insulator material on the focus mask to accumulate charge. Such charge accumulation is undesirable because it may interfere with the ability of the focus mask to accurately direct the electron beams toward the color-emitting phosphors formed on the screen, as well as cause HV flashover between the conductive lines of the focus mask.
Thus, a need exists for suitable insulating materials that overcome the above-mentioned drawbacks.
The present invention relates to a color cathode-ray tube (CRT) having an evacuated envelope with an electron gun therein for generating an electron beam. The envelope further includes a faceplate panel having a luminescent screen with phosphor lines on an interior surface thereof. A focus mask, having a plurality of spaced-apart first conductive lines, is located adjacent to an effective picture area of the screen. The spacing between the first conductive lines defines a plurality of slots substantially parallel to the phosphor lines on the screen. Each of the first conductive lines has a substantially continuous insulating material layer formed on a surface thereof. A plurality of second conductive lines are oriented substantially perpendicular to the plurality of first conductive lines and are bonded thereto by the insulating material layer. A cap layer is formed over the plurality of second conductive lines and the insulating material. The cap layer is a semiconducting layer that is used to prevent charge accumulation on the insulating material layer.